Initially trained by Último Dragón and making his debut in August 2004, Okada spent his first years in professional wrestling working in Mexico, before returning to Japan and making NJPW his home promotion in mid-2007. Originally working as a junior heavyweight, Okada graduated to the heavyweight division in April 2008, with limited success. In February 2010, NJPW sent Okada on a learning excursion to American promotion Total Nonstop Action Wrestling (TNA), where he ended up spending the next twenty months, mainly performing on the promotion's secondary television program, Xplosion. From January to March 2011, now performing under the ring name Okato, he was featured on TNA's primary television program, Impact!, as Samoa Joe's sidekick in his rivalry with D'Angelo Dinero.

Okada's run with TNA ended in October 2011 and he returned to NJPW in January 2012, repackaged as "Rainmaker" (レインメーカー,Reinmēkā), complete with a new look and a villainouspersona. Just a month later, Okada defeated Hiroshi Tanahashi to win NJPW's top title, the IWGP Heavyweight Championship, which he would hold for four months before losing it back to Tanahashi. The following August, Okada won NJPW's premier tournament, the G1 Climax. At the end of the year, the Tokyo Sports magazine named Okada the 2012 MVP in all of Japanese professional wrestling. The following year, Okada first won the New Japan Cup in March and then regained the IWGP Heavyweight Championship from Tanahashi in April. After a thirteen-month reign, Okada lost the title in May 2014. Three months later, he won his second G1 Climax. Okada has since won the IWGP Heavyweight Championship two more times and headlined NJPW's biggest annual event—the January 4 Tokyo Dome Show—five times (2013, 2015, 2016, 2017 and 2018).

As a child, he lived and attended a primary school in Anjō. However, before completing primary school, Okada was lured by the nature in his mother's hometown in the Gotō Islands in Nagasaki Prefecture and chose to complete the rest of his primary education in a special boarding school there.[10] Upon graduation, he returned to Anjō.

In middle school, Okada joined the school's baseball and track team. Although he did not stand out as a baseball player, Okada was able to win first place in a regional 100 meter dash competition. His reputation as a sprinter was good enough to be scouted by high school recruiters.[10] He was exposed to professional wrestling for the first time when one of his older brothers happened to borrow a New Japan Pro-Wrestling (NJPW) video game from his friend.[10]

Okada made his TNA debut at the February 16, 2010, tapings of Impact!, losing to Alex Shelley in a dark match.[18] At the March 9 tapings, Okada was defeated by Jay Lethal in another dark match.[19] On March 20, Okada made his debut for Jersey All Pro Wrestling (JAPW) at Wild Card VI, where he was defeated by fellow TNA wrestler Samoa Joe.[20] Okada's dark matches for TNA continued on March 23 with a loss against Daniels.[21] On April 6, Okada, using only his last name, competed in his first televised TNA match when he and Homicide were defeated by Generation Me (Jeremy and Max Buck) in a tag team match, which was later broadcast on the Xplosion television program and the company's official website and YouTube channel.[22][23] That same week, Okada also began wrestling at TNA's live events.[4] On May 4, Okada and Homicide were defeated in another Xplosion match by Ink Inc. (Jesse Neal and Shannon Moore).[24] On May 17, X Division ChampionDouglas Williams defeated Okada in a non-title Xplosion match.[25] On July 15, Okada made his first appearance on Impact!, running out to the ring in an attempt to stop former ECW wrestlers from taking over the show.[26] At the August 9 tapings, Okada picked up his first victory in TNA, defeating Kid Kash in a dark match.[27] On the October 8 Xplosion, Okada formed a tag team with compatriot Kiyoshi, but the two of them were then defeated in their first match together by Ink Inc.[28] On the November 26 Xplosion, Okada was defeated by Rob Terry.[29] On the December 17 Xplosion, Okada was defeated by Stevie Richards.[30] Okada and Kiyoshi had a rematch with Ink Inc. at the December 7 tapings of Xplosion, but were once again defeated.[31]

On January 20, 2011, Okada turned into a fan favorite as he made his second appearance on Impact!, when he was revealed as the camera man whom Samoa Joe had hired to follow D'Angelo Dinero in order to expose his lies about helping the needy.[32] During the appearance, Okada debuted a new look inspired by Kato from The Green Hornet series.[33] Okada, now renamed Okato, made his first TNA pay-per-view appearance at Against All Odds on February 13, preventing Dinero from leaving the ring during his match with Joe. After losing the match, Dinero attacked both Okato and Joe.[5][34] Okato made his Impact! in-ring debut on March 24, when he defeated Dinero via disqualification.[35] The match concluded Okato's participation in the feud between Joe and Dinero and he subsequently returned to performing under his real surname. On the June 21 Xplosion, Okada was defeated by Alex Shelley in the first round of the Xplosion Championship Challenge.[36] On October 13, his profile was removed from TNA's roster page.

TNA's handling of Okada was reportedly one of the reasons NJPW ceased the relationship between the two promotions shortly afterwards.[37][38][39] Despite not being used by TNA, Okada has stated that he felt that his time in the promotion was beneficial to him as he learned he needed more than just a good match—he needed a character. According to Okada, in Japanese professional wrestling "there is no character – it's fight, fight, fight", but TNA's agents kept telling him that he needed a character, which led to him creating the "Rainmaker" persona upon his return to NJPW.[39] In October 2017, it was reported that while representatives of the American promotion, now known as Impact Wrestling, were visiting Japan, attempting to revive the relationship between their company and NJPW, they specifically apologized to Okada for his treatment.[40]

On January 4, Okada defeated Yoshi-Hashi in his return match and then challenged Hiroshi Tanahashi to a match for the IWGP Heavyweight Championship following the show's main event.[52] At the following day's press conference, where the title match was made official, Okada revealed that he had joined Chaos, NJPW's top villainousstable, enlisting new stablemate Gedo as his manager and spokesperson.[53] Adopting the new villainous persona of "Rainmaker", Okada changed the Japanese writing of his ring name from "岡田かずちか" to "オカダ・カズチカ".[1][2][50] Okada described his new persona as a combination of the three professional wrestling styles he had learned, stating that he took his dropkick from Mexico, his "fighting spirit" from Japan and the "TV and the entertainment" from the United States.[39] In the month leading to the title match, Okada went on a main event win streak, which included pinning Tanahashi in a tag team match on January 29.[54][55][56] On February 12 at The New Beginning, Okada defeated Tanahashi to win the IWGP Heavyweight Championship for the first time.[57] Okada made his first title defense on March 4, defeating Tetsuya Naito in the main event of NJPW's 40th anniversary event.[58] On May 3 at Wrestling Dontaku 2012, Okada defeated 2012 New Japan Cup winner and reigning IWGP Intercontinental Champion Hirooki Goto to make his second successful title defense.[59] On June 16 at Dominion 6.16, Okada lost the IWGP Heavyweight Championship back to Hiroshi Tanahashi, ending his reign at 125 days.[60]

On August 1, Okada entered his first G1 Climax tournament.[61] In the tournament, Okada wrestled in the same block as Chaos leader Shinsuke Nakamura and, on August 5, was defeated by Nakamura, who effectively solidified his spot as the group's leader in the process.[62] However, Okada bounced back from the loss, winning five of his eight round-robin stage matches and finished at the top of his block, advancing to the finals of the tournament.[63][64] In the finals on August 12, Okada defeated Karl Anderson to win the 2012 G1 Climax.[63][64] Breaking Masahiro Chono's record for the youngest G1 Climax winner in history, Okada announced that he wanted his shot at the IWGP Heavyweight Championship on January 4, 2013, at Wrestle Kingdom 7 in Tokyo Dome.[65] Okada signed a contract for the Tokyo Dome match on September 6, making him the official number one contender to the IWGP Heavyweight Championship at NJPW's biggest event of the year.[66][67] However, before January 4, Okada would have to defend his contract as if it were a championship.[68] On October 8 at King of Pro-Wrestling, Okada made his first successful defense of the contract against Karl Anderson.[69][70] On November 11 at Power Struggle, Okada made another successful defense against Hirooki Goto. Later in the event, after Hiroshi Tanahashi had successfully defended the IWGP Heavyweight Championship against Yujiro Takahashi, the Tokyo Dome title match between him and Okada was made official.[71][72] From November 20 to December 1, Okada took part in the round-robin portion of the 2012 World Tag League, alongside stablemate Yoshi-Hashi under the team name "Chaos Ride the Lightning".[73] The team finished with a record of three wins and three losses, with a loss to Sword & Guns (Hirooki Goto and Karl Anderson) on the final day, costing them a spot in the semifinals of the tournament.[74][75] On December 10, Tokyo Sports named Okada the 2012 MVP in all of puroresu.[76][77] His match with Hiroshi Tanahashi from June 16 was also named the Match of the Year.[76][77] On January 4, 2013, at Wrestle Kingdom 7 in Tokyo Dome, Okada failed in his title challenge against Tanahashi.[78][79] On January 15, Okada publicly dismissed rumors that he was going to be signing with WWE and instead announced that he had just signed a contract extension with NJPW.[80]

In February, Okada led Chaos to a war with NJPW's other heel stable, Suzuki-gun,[81] which built to a match on February 10 at The New Beginning, where Okada, positioned as the face, was defeated by the stable's leader Minoru Suzuki, following interference from Taichi.[82] In preparation for the 2013 New Japan Cup, Okada announced that he had created a new submission finishing maneuver, the Red Ink, in order to win the tournament.[83] On March 11, he used the Red Ink to defeat Suzuki-gun member and IWGP Tag Team ChampionLance Archer in his first round match.[84][85] Six days later, Okada advanced to the semifinals of the tournament with a win over Karl Anderson.[86] On March 23, Okada first defeated Chaos stablemate Toru Yano in the semifinals and then Hirooki Goto in the finals to win the 2013 New Japan Cup and once again become the number one contender to Tanahashi's IWGP Heavyweight Championship.[87][88][89] On April 7 at Invasion Attack, Okada defeated Tanahashi to win the IWGP Heavyweight Championship for the second time.[90][91][92] On May 3 at Wrestling Dontaku 2013, Okada made his first successful title defense against Minoru Suzuki.[93][94] His second successful defense took place on June 22 at Dominion 6.22 against Togi Makabe.[95][96] On July 20, Okada made his third successful title defense against IWGP Junior Heavyweight ChampionPrince Devitt.[97][98][99][100] From August 1 to 11, Okada took part in the 2013 G1 Climax,[101] where he opened by losing three of his first four matches.[102] After bouncing back to a three-match win streak and a time limit draw with Hiroshi Tanahashi,[103] Okada finished his tournament with a loss against Satoshi Kojima, which meant that he was eliminated from the tournament.[104][105] On August 18, Okada made a rare appearance outside of NJPW, when he took part in the DDT Pro-Wrestling promotion's annual Ryōgoku Peter Pan event, defeating Kota Ibushi in a special non-title match.[106][107][108] On September 29 at Destruction, Okada avenged the loss from G1 Climax by defeating Satoshi Kojima for his fourth successful defense of the IWGP Heavyweight Championship.[109][110]

On October 14 at King of Pro-Wrestling, Okada made his fifth successful title defense against Hiroshi Tanahashi in what Tanahashi claimed would be his final challenge for the title.[111][112][113] With the win, NJPW claimed that Okada had taken over Tanahashi's spot as the "ace" of the promotion.[111] On November 9 at Power Struggle, Okada defeated Karl Anderson in a rematch of the 2012 G1 Climax finals for his sixth successful title defense.[114][115][116] Okada and his next challenger, 2013 G1 Climax winner Tetsuya Naito, faced off on November 23 during the first day of the 2013 World Tag League in a match, where Okada and Yoshi-Hashi were victorious over Naito and La Sombra.[117] Okada and Yoshi-Hashi however managed to win only one of their five remaining matches in the tournament and finished second to last in their block, failing to advance to the semifinals.[118] Following a disappointing fan reaction to a confrontation between Okada and Naito, NJPW announced that fans would get to vote whether they or Shinsuke Nakamura and Hiroshi Tanahashi for the IWGP Intercontinental Championship would be the true main event of the Tokyo Dome show.[119][120] When the results were released on December 9, Okada and Naito had gotten only half the votes Nakamura and Tanahashi had gotten and, as a result, lost their main event spot for NJPW's biggest show of the year.[121][122] That same day, Okada became the first wrestler in 25 years to win back-to-back MVP awards from Tokyo Sports.[123][124] On January 4, 2014, at Wrestle Kingdom 8 in Tokyo Dome, Okada defeated Naito for his seventh successful title defense.[125][126] Okada's eighth successful title defense took place on February 11 at The New Beginning in Osaka, where he defeated Hirooki Goto.[127][128] On April 6 at Invasion Attack 2014, Okada found himself a new challenger in Bullet Club's newest member, the debuting A.J. Styles, who claimed that Okada was still the same "young boy" (rookie) he had known in TNA.[129][130] On May 3 at Wrestling Dontaku 2014, Okada's thirteen-month reign as the IWGP Heavyweight Champion came to an end, when he lost the title to Styles in his ninth defense, after Yujiro Takahashi turned on him and Chaos and joined Bullet Club.[131][132][133]

Okada in May 2014

In May, Okada took part in NJPW's North American tour, during which he received a rematch for the IWGP Heavyweight Championship. On May 17 at War of the Worlds in New York City, Okada unsuccessfully challenged Styles for the title in a three-way match, which also included Michael Elgin, whom Styles pinned for the win.[134] Okada received another shot at the title on May 25 at Back to the Yokohama Arena, but was again defeated by Styles.[135][136] From July 21 to August 8, Okada took part in the 2014 G1 Climax, where he won his block with a record of eight wins and two losses, which included a win over Styles,[137] advancing to the finals.[138][139] On August 10, Okada defeated Chaos stablemate Shinsuke Nakamura to win the 2014 G1 Climax.[140][141] On September 21 at Destruction in Kobe, Okada teamed with Yoshi-Hashi to unsuccessfully challenge Bullet Club's Doc Gallows and Karl Anderson for the IWGP Tag Team Championship.[142][143] Two days later at Destruction in Okayama, Okada successfully defended his IWGP Heavyweight Championship number one contender's contract against Karl Anderson.[144][145] On October 13 at King of Pro-Wrestling, Okada made another successful defense of his contract against Tetsuya Naito.[146][147] The following month, Okada once again teamed up with Yoshi-Hashi for the 2014 World Tag League.[148] The team finished their block with a record of four wins and three losses, failing to advance to the finals.[149] On January 4, 2015, at Wrestle Kingdom 9 in Tokyo Dome, Okada received his shot at the IWGP Heavyweight Championship, but was defeated by the defending champion, Hiroshi Tanahashi.[150][151] Okada then started a stoyline, where the loss to Tanahashi had broken him both physically and mentally, causing him to enter a slump.[152] This led to a rivalry between him and Bullet Club's Bad Luck Fale, who scored several pinfall wins over Okada, including in the first round of the 2015 New Japan Cup.[153][154] Okada finally defeated Fale in a singles match on April 5 at Invasion Attack 2015, after which he announced his intention of regaining the IWGP Heavyweight Championship by attacking A.J. Styles at the conclusion of the event.[155][156]

On July 5 at Dominion 7.5 in Osaka-jo Hall, Okada defeated Styles to win the IWGP Heavyweight Championship for the third time.[157][158] From July 23 to August 15, Okada took part in the 2015 G1 Climax.[159] He entered the final day with a chance to advance from his block, but a loss against Chaos stablemate Shinsuke Nakamura cost him a spot in the finals, giving him a record of seven wins and two losses.[160] On August 16, Okada had a staredown with Genichiro Tenryu, who chose him to be his opponent in his retirement match.[161] On November 15 at Revolution Final, Okada defeated Tenryu in his retirement match.[162][163] On December 7, Okada won his third MVP award from Tokyo Sports, while his match with Tenryu was named the Match of the Year.[164][165] With the win, Okada became only the fifth three-time MVP award winner.[166] In December 2015, Okada signed a one-year contract extension with NJPW. However, following A.J. Styles and Shinsuke Nakamura's departures from the promotion the following month, NJPW owner Takaaki Kidani announced that the promotion was scrapping the one-year contract system and was looking to offer Okada, their top priority, a new five-year ¥200 million contract.[167] On January 4, 2016, Okada defeated 2015 G1 Climax winner Hiroshi Tanahashi in the main event of Wrestle Kingdom 10 in Tokyo Dome to retain the IWGP Heavyweight Championship and become the new ace of the promotion, the match at that time was the longest in the history of the January 4 Dome Show .[168]

Okada made his third successful title defense on February 11 at The New Beginning in Osaka against Hirooki Goto.[169] On April 10 at Invasion Attack 2016, Okada lost the IWGP Heavyweight Championship to 2016 New Japan Cup winner Tetsuya Naito, following outside interference from Naito's Los Ingobernables de Japon stablemates Bushi, Evil and the debuting Sanada.[170] Okada gained revenge on Sanada by defeating him on May 3 at Wrestling Dontaku 2016.[171] This led to a rematch with Naito on June 19 at Dominion 6.19 in Osaka-jo Hall, where Okada won the IWGP Heavyweight Championship for the fourth time.[172][173] From July 18 to August 12, Okada took part in the 2016 G1 Climax, where he finished tied second in his block with a record of five wins, one draw and three losses.[174] A 30-minute time limit draw against Hiroshi Tanahashi on the final day eliminated both men from advancing to the finals.[175] During the G1 Climax, Okada was defeated by Pro Wrestling Noah representative Naomichi Marufuji, which led to his first title defense following the tournament on October 10 at King of Pro-Wrestling, where Okada retained the IWGP Heavyweight Championship against Marufuji, thus setting up the main event of Wrestle Kingdom 11 in Tokyo Dome between Okada and the 2016 G1 Climax winner Kenny Omega.[176] On December 14, Okada became the second wrestler to win three consecutive Match of the Year awards from Tokyo Sports for his 2016 G1 Climax opener against Naomichi Marufuji.[177]

On October 22, Okada became the longest-reigning IWGP Heavyweight Champion in history by breaking the previous record of 489 days, held by Shinya Hashimoto. On January 3, 2018, Okada also broke Hiroshi Tanahashi's record of 1,358 combined days as champion.[198] The following day at Wrestle Kingdom 12, Okada defeated Tetsuya Naito to retain the title.[199] On February 10 at The New Beginning in Osaka, Okada defeated Sanada to retain the championship for the tenth time.[200] On March 21, Okada was challenged for the title by New Japan Cup winner Zack Sabre Jr. and at Sakura Genesis went on to defeat Sabre Jr. to tie Hiroshi Tanahashi's record for most successful title defenses in one reign at 11 defenses. After the match, Okada would be confronted by Tanahashi, indicating a future match for the title. They would meet at Wrestling Dontaku 2018, where Okada would defeat Tanahashi for his record-breaking 12th successful title defense,[201] breaking Tanahashi's record of 11, and earning a 5 1/2 Star rating from Wrestling Observer Newsletter. His next challenger was then revealed to be Kenny Omega, having been chosen due to Okada's frustration with having one win, draw, and loss against him. In their fourth match, they competed in a two out of three falls match at Dominion 6.9 in Osaka-jo Hall (with no time limit to ensure there is no possibility of a draw as in their second singles match at Dominion 6.11), where Omega would defeat Okada 2–1 to win the championship after a 65 minute match, ending Okada’s record-breaking championship reign at 720 days.[202]

Okada then entered the 2018 G1 Climax, where he finished with a record of six wins, one draw and two losses, exactly the same as the previous year's event, failing to advance to the finals.[203] The event saw a change of image for Okada following the defeat by Omega, with his hair dyed red and portraying an indifferent attitude.[204] This caused him to lose his first two matches against Jay White and Bad Luck Fale,[205][206] although he would go on to the win the rest of the matches in his block, until the last one; another 30-minute time limit draw against Tanahashi.[203] At the 2018 G1 Climax Finals, Okada parted ways with his longtime manager Gedo.[207] Unsatisfied by their draw in the G1, Tanahashi opted to defend the contract for his Wrestle Kingdom 13 title shot against Okada. On September 23 at Destruction in Kobe, Okada was defeated by Tanahashi. Afterwards, he was attacked by Jay White before Gedo, his former manager, came out seemingly to stop him, only to betray Okada by hitting him in the back with a chair. [208] This led to a match between White and Okada at Wrestle Kingdom 13, where he was defeated. In March, Okada competed in the New Japan Cup. He would defeat Michael Elgin in Round 1, and fellow Chaos members Mikey Nicholls, Will Ospreay, and Tomohiro Ishii in Round 2, the Quarterfinals, and Semi-Finals, respectively. He would go on to defeat Sanada in the finals of the tournament and win his second New Japan Cup. In doing so, he won the opportunity to challenge Jay White at New Japan/Ring of Honor joint show, G1 Supercard, for the IWGP Heavyweight Championship. On April 6, Okada defeated White to win the title for the fifth time.

Along with fellow NJPW wrestler Shinsuke Nakamura, Okada is featured in the Japanese music video for Pharrell Williams' song Happy, released in May 2014.[210] In 2015, Okada voiced a character in the World Trigger anime series.[211] The following year, he voiced a character in another anime, Future Card Buddy Fight 100.[212] Okada, along with fellow NJPW wrestlers Hiroshi Tanahashi, Hiroyoshi Tenzan, Satoshi Kojima, Tetsuya Naito and Toru Yano, appears as a member of the gang Justis in the 2016 video game Yakuza 6: The Song of Life.[213] In January 2017, it was announced that the Tekken 7: Fated Retribution video game would feature Okada's in-ring costume as an alternate outfit for the character King. When equipped, King performs Okada's finishing maneuver, the Rainmaker, as his "Rage Art" move.[214] The Okada-geared King was featured on the September 12, 2017 episode of WWE's 205 Live program.[215]

Okada was engaged to TV Asahi presenter Yoko Mori, whom he had been in a relationship with from 2013 to 2017.[216] In August 2014, after his uncle and cousin had both been diagnosed with cancer, Okada established the "Rainmaker Kikin" ("Rainmaker Fund") to battle children's cancer. For every match Okada won, he pledged to donate ¥30,000 (the equivalent of US$378).[217][218]